It is known for a nozzle in hot runner injection molding machines to include a thermally conductive body and a thermally conductive tip. Furthermore, it is known for the nozzle to include a separate tip retainer that joins to the nozzle body and retains the tip in the nozzle body. The tip retainer is also typically used to seal between the nozzle and the mold cavity plate to which the nozzle transfers melt. Because the mold cavity plate is usually cooler than the tip, the tip retainer is typically made from a material that is less thermally conductive than the tip itself.
An example of such a nozzle construction is shown in U.S. Pat. No. 5,299,928 (Gellert). By making the tip retainer out of a less thermally conductive material than that of the tip itself, the efficiency of the nozzle to transfer heat from the heater to the melt is reduced, sometimes significantly.
Thus a need exists for new nozzle constructions that have high heat transfer efficiency.